Is C Missing a `round()` Function, and How Can It Be Implemented?

Floating-Point Rounding in C : The Absence of round()

While functions like ceil() and floor() are available in math.h for rounding floating-point numbers, the standard C library lacks a dedicated round() function. This has led to the question of whether round() is missing or simply exists under a different name in the C 98 standard.

Implementation of a Custom round() Function

Since round() is not natively provided, users have resorted to creating their own implementations. One such implementation, based on the round-half-up method, is:

double round(double d) {
  return floor(d + 0.5);
}

However, it's important to note that this implementation may not always produce the desired results, as it rounds up numbers that are exactly 0.5 away from an integer to the nearest even integer.

Alternative Rounding Methods

Other rounding methods exist, such as round-to-even, which provides a less biased rounding approach and is preferred for high-volume rounding.

Inclusion in C 11

Fortunately, C 11 introduced built-in round() functions, including std::round, std::lround, and std::llround, which provide standard rounding behavior for various data types. These functions offer more robust and efficient implementation than custom solutions.

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